1. Field of the Invention
The present invention relates generally to waveguide connectors, and more particularly, but not by way of limitation, to a method of and apparatus for connecting waveguides of differing cross-sectional shapes one to the other.
2. Description of Related Art
The use of waveguides is commonplace for transmitting electromagnetic waves from one point to another. One of the more extensive commercial uses is the transmission of electromagnetic signals from transmitting or receiving equipment. This transmission may occur, for example, between an equipment shelter and an antennae, often mounted on a tall tower. In general, the waveguide consists of a hollow metallic tube of defined cross-section, uniform in extent in the direction of propagation. Within the hollow tube, the electric and magnetic fields are confined, and, since the tubes are normally filled with air, dielectric losses are minimal. Commercially available waveguides have a variety of cross-sectional shapes, including, for example, rectangular, circular and elliptical. Such waveguide shapes are, for example, disclosed in U.S. Pat. No. 3,822,411 to Merle and U.S. Pat. No. 4,047,133 to Merle.
Typically, waveguides must be coupled at some point. Both the design of the waveguide, as well as coupling systems for use therewith, are critical to the efficiency of the overall system and thus certain design parameters must be applied. For example, commonly-used rectangular waveguides may have an aspect ratio of approximately 0.5. This aspect ratio is well known to preclude the generation of field variations with height and their attendant unwanted modes. It is similarly well-known to securely mount a waveguide within a waveguide connector in order to prevent reflection losses and impendence mismatches. Reliable and secure mountings are not, however, always easy to accomplish. It is thus critical to provide the appropriate coupling mechanism and methods of assembly for use therewith when linking waveguides one to the other. This design concern is particularly relevant when joining waveguides of differing cross-sectional shape.
Waveguide connectors that are exemplary of prior designs are disclosed in U.S. Pat. No. 3,818,383 to Willis (the ""383 Patent) and U.S. Pat. No. 3,784,939 to Maeda, et al. (the ""939 Patent). The ""383 Patent discloses an elliptical-to-rectangular waveguide transition that employs concave top and bottom walls of generally elliptical form and side walls of no concavity. Non-linear tapering of cross-sectional dimensions are employed to minimize reflections at the ends of the transition. The ""939 Patent discloses a waveguide connector that is connected to a waveguide flared at its end by positioning a pressure member loosely encompassing the waveguide that is used to press the flared end of the waveguide against the connector so that paths of the waveguide and the connector are precisely aligned. Each of these connectors requires a flange and/or flaring of the waveguide(s) in order to achieve connection therebetween. As referenced above, the coupling of waveguides of differing shapes one to the other involves a myriad of design issues.
Another example of a connector for joining a rectangular waveguide to an elliptical waveguide is set forth and shown in U.S. Pat. No. 4,540,959 assigned to the assignee of the present invention (the ""959 Patent), which patent is incorporated herein by reference. As set forth in the ""959 Patent, an inhomogeneous waveguide connector may be designed to provide a low return loss over a wide bandwidth. The waveguide connector of the ""959 Patent utilizes a stepped transformer formed within a connector passageway of a flanged connector for directly joining a rectangular waveguide and mounting flange assembly to an elliptical waveguide and mounting flange assembly.
The transformer, as therein described, includes multiple steps, all of which have inside dimensions small enough to cut off the first excitable higher order mode in a preselected frequency band. It may be seen that each step of the transformer includes an elongated transverse cross-section which is symmetrical about mutually perpendicular transverse axes which are common to those of the rectangular and elliptical waveguides, the dimensions of the elongated transverse cross-section increasing progressively from step to step in all four quadrants along the length of the transformer, in the direction of both of the transverse axes, so that both the cutoff frequency and the impedance of the transformer vary monotonically along the length of the transformer.
In addition to the functional efficiency, the waveguide connector of the ""959 Patent is relatively easy to fabricate by machining so that it can be efficiently and economically manufactured with precise tolerances, and without costly fabricating techniques. Since the connector therein described incorporates a stepped transformer, the return loss decreases as the number of steps is increased so that the connector can be optimized for minimum length or minimum return loss, or any desired combination of the two, depending upon the requirements of any given practical application.
As seen in the waveguide connector designs discussed above, a significant functional and structural aspect of waveguide connectors is mechanical securement of the waveguides to the waveguide connector as well as the waveguide connectors to each other. The ""959 Patent provides a good example of mating structural flanges. Such mating flanges have been commonplace for many years for the connection of waveguides one to the other. Typically, one of two mating flanges is secured to an end of a first waveguide in such a way that it will mate with the flange of a second waveguide also mounted directly to an end thereof or to the flange of a stepped transformer joining said waveguides as set forth in the ""959 Patent. The mating flanges are then aligned and assembled one to the other, typically with threaded fasteners or the like.
Mating flanges are, by definition, constructed for coupling one to the other. The same is inherently untrue of the hollow tubes that form the waveguides themselves. While it is known how to securely mount and solder a rectangular waveguide to a waveguide mounting flange, the methods of and apparatus for reliable mounting of elliptical waveguides to waveguide connectors is not as well developed a technology. The coupling of elliptical waveguides to the requisite waveguide connector is therefore an area of concern from both engineering and quality control standpoints and also from a cost perspective. In that regard, flaring of portions of the elliptical waveguide, as described above, has been one approach for the mechanical coupling of the waveguide to the mounting flange. The flaring must typically be performed before a waveguide connector can be used to join the waveguide sections together. Such flaring is often performed in order to increase the mechanical strength of the interface between the waveguide connector and the waveguide. The flaring is also used to insure electrical continuity between the waveguide connector and the waveguide. It may be appreciated that the flaring of waveguides and related operations necessary in order to connect waveguides together in such a manner increases labor and materials costs.
It would be a distinct advantage, therefore, to provide a waveguide connector and method for connecting elliptical waveguides that could be used without the necessity of a flaring operation and/or related mechanical steps that are inherently less reliable than the soldered engagement of rectangular waveguides to their associated mounting flanges. It would thus be advantageous to provide a method of and apparatus for reliably connecting elliptical waveguides one to the other, as well as to rectangular waveguides and waveguides of other shapes, utilizing a connector that maximizes structural integrity without the prior art problems of mechanical interconnection and the associated cost inefficiencies associated therewith. It would further be a distinct advantage to provide an elliptical waveguide as described above with a stepped transformer formed therein.